Cholecystokinin (CCK) is a peptide common to gut and brain. It is very abundant in brain and may be a neurotransmitter or neuromodulator. CCK is abundant in the striatum and because of its anti-tremor activity, it has been suggested that CCK may plat a role in regulation of extrapyramidal motor activity. Observed decreases in CCK levels in brain and CSF in Parkinson's patients and in brain in Huntington's patients suggest alteration in CCK function in these neurological diseases. The long term objective of this research is to understand the role of CCK in the striatum. Investigating the regulation of CCK release in the striatum may lead to insight into how transmitter inbalance in Huntington's and Parkinson's disease may influence striatal neurons and how this may be reversed pharmacologically. Studies on the biosynthesis of CCK in the hippocampal slice and in CCK producing cell lines will provide more information about how CCK is made and what factors might modify this. This information may lead to better therapeutic regulation of the symptoms of Parkinson's disease. The specific aims of the proposal are: Aim 1: Using rat hippocampal slices and CCK-producing cell lines, we will establish the temporal order of the processing of pro CCK to CCK delta and examine if depolarization-induced release of CCK alters the rate of CCK synthesis. Aim 2: Using CCK-producing cell lines created by site-directed mutagenesis of rat cDNA transfected into the ATt20 cell line, we will examine how modification of the sequence of pro CCK alters its sulfation and cleavage. Aim 3: Using synaptosome preparations from rat brain and secretory vesicle preparations from the CCK-producing cell lines, we will characterize and purify enzymatic activity which specifically cleaves CCK 33 at a monobasic Arg-Asp site to produce CCK delta. Aim 4: Using rat brain slices, we will continue our studies on the modulation of cCK release, focusing on the identity and possible mechanism of action of endogenous inhibitory and stimulatory factors.